Researchers Make Energy-Burning Fat

July 29, 2009

Researchers Make Energy-Burning Fat

Could injections of brown fat treat obesity?

This is a microscope image of brown fat (e-BAT, or engineered Brown Adipose Tissue) created by adding a key control switch to skin cells of mice. Presence of green-stained objects (droplets of oil stored in the cell) confirms the skin cells have been converted to brown fat-producing cells. Blue objects are cell nuclei.
Credit: Shingo Kajimura, Ph.D., Dana-Farber Cancer Institute

Researchers have developed a recipe for making brown fat, an energy-burning
type of fat found mostly in infants and hibernating animals, and discovered
that when injected into mice, it caused the cells to develop into brown fat
tissue that burned excess energy. However, it’s not yet clear whether the fat
transplant can prevent these animals from gaining weight when on a high-calorie
diet. The research was reported online today in the journal Nature.

White fat–the culprit behind beer bellies and dimpled thighs–stores excess
energy from a person’s diet. High levels of white fat, especially around the
abdomen, can increase the risk for heart disease and diabetes. The primary role
of brown fat, in contrast, is to generate heat, protecting newborns from the
cold, for example. Scientists previously thought that only young animals had
significant amounts of this tissue, but recent research using positron-emission
tomography has shown that adults have a surprising amount of brown fat around
the neck and chest. Because these cells burn calories, scientists have been
searching for ways to turn up their activity as a potential treatment for
obesity.

In the recent study, Bruce
Spiegelman and colleagues at the Dana Farber Cancer Institute identified
two proteins that work together to trigger development of brown fat. When
researchers engineered genes for these two proteins into both mouse and human
skin cells, the cells developed into brown fat.

The scientists then transplanted these
synthetic brown fat precursors, known as eBAT (engineered [brown adipose tissue]),
into adult mice to augment their innate stores of brown fat. Tests showed that
the brown fat transplants were burning caloric energy at a high rate – energy
that otherwise would have been stored as fat in white adipose tissue.

“Since brown fat cells have very
high capacity to dissipate excess energy and counteract obesity, eBAT has a
very high potential for treating obesity,” said Shingo Kajimura, PhD, lead
author of the paper. “We are currently working on this.”

… The
experiments did not test whether the extra brown fat actually protected the
mice from becoming obese.